Hi, happy to answer your questions - this might get a bit detailed, so I’ll put a summary at the end.
Yes, the seams between tiles can be fixed, but will require some work. Or if you want to get the bottom image’s faceted style, you can actually skip all of that work.
A bit of background first.
The different types of shading behavior you’re seeing here are due to different normals. A normal is a vector that points away from the surface, that’s used by rendering when shading the faces. In EditableMesh, at each vertex, you can have a normal vector that is automatically computed, or a normal vector that is manually set. The default is automatically computed.
EditableMesh’s faces store 4 ids per corner - a vertex id, a normal id, a uv id, and a color id. When you call :AddTriangle, you only specify the vertex ids. AddTriangle will either create new ids for normal, uv, and color, or if the vertex is already part of a face, it will reuse ids from that vertex on that face.
So, if you were to run some code like:
local fid1 = emesh:AddTriangle(vid1, vid2, vid3)
local fid2 = emesh:AddTriangle(vid2, vid1, vid4)
You’d get something that looks like this:
You can see that the faces f1 and f2 share vertices, v1 and v2. Also, on those vertices, they share the same normal, uv, and color ids.
When a normal id is an automatically generated normal, EditableMesh looks at each face corner that’s using that normal id, computes the normal at that corner (using a cross product), and then averages together all of the normals on all of the face corners.
If you combine those two behaviors, the default behavior is that you get a single averaged normal vector at each vertex, which gives you the smooth look of most of the terrain in your first image.
However, between the tiles, the different EditableMeshes don’t know that they’re supposed to be connected. When computing the automatic normals, there’s not a good way for them to know that the normal vectors should be averaged out between the two EditableMeshes.
You can do this manually if you know which vertex ids on each mesh correspond with each other, something like:
local normal1 = emesh1:GetNormal(nid_on_mesh1)
local normal2 = emesh2:GetNormal(nid_on_mesh2)
local avg = (normal1 + normal2).Unit
emesh1:SetNormal(nid_on_mesh1, avg)
emesh2:SetNormal(nid_on_mesh2, avg)
Please note that this will change the normal id on both meshes from automatically computed to manually set, so if the mesh vertices near the border change local position, you’ll probably want to redo this step.
However, I have some good news about the second image. Not only is this possible, but if you go for this style, you don’t have to bother with making the normals between the terrain tiles match.
The trick to getting that faceted appearance is that you want a single normal per face, instead of averaging the normals on a vertex.
If you run something like:
local fid1 = emesh:AddTriangle(vid1, vid2, vid3)
local fid2 = emesh:AddTriangle(vid2, vid1, vid4)
local nid5 = emesh:AddNormal()
emesh:SetFaceNormals(fid1, {nid5, nid5, nid5})
local nid6 = emesh:AddNormal()
emesh:SetFaceNormals(fid2, {nid6, nid6, nid6})
emesh:RemoveUnused()
You’ll get something like this:
This will give you faceted rendering like in your second image.
So, TL;DR, if what you want is rendering like the bottom image, the easiest way is to use something like:
local function addSharpTriangle(emesh, vid1, vid2, vid3)
local fid = emesh:AddTriangle(vid1, vid2, vid3)
local nid = emesh:AddNormal()
emesh:SetFaceNormals(fid, {nid, nid, nid})
return fid
end
and then after you’re done making the mesh, call emesh:RemoveUnused(), to clean up unused ids and save a bit of memory.
